The execution of North Korean leader Kim Jong-un's once-powerful uncle has made relations between the two Koreas harder to predict, South Korean President Park Geun-hye said, pledging to maintain airtight security against possible provocations.

In an article contributed to the Project Syndicate, Park also said she will stick to her trademark trust-building policy toward the communist nation to lay the groundwork for unification on the divided Korean Peninsula.

"The recent North Korean political situation following the purge of Jang Song-thaek, known as the second man, has further spurred concerns of Koreans and the international community, for it has put inter-Korean relations at a more unpredictable situation," Park said in the article.

Jang's execution has prompted fears of instability in the North's leadership, though some analysts have said the execution demonstrates that Kim has consolidated power and is firmly in charge. Concerns have also grown over the direction in which the unpredictable leader will take the nuclear-armed nation.

Park has repeatedly called the North's situation "grave," warning that Pyongyang could attempt "reckless provocations" in an attempt to divert domestic attention from the execution. She has also ordered the government to make preparations for all possible contingencies and the military to beef up its vigilance.

"We will pave the way to peace and unification on the Korean Peninsula. My government will maintain a strong deterrent capability, because airtight security constitutes the foundation of genuine peace," Park said in the article.

"From this point, the government will strive to forge sustainable peace through dialogue, exchanges and cooperation, so as to achieve unification that improves the quality of life and happiness of all Koreans," she said.

Park also pledged to work closely together with the international community, saying that Korean unification should be achieved with the blessings of neighboring countries, though it is "certainly a matter for the Korean people to decide."

She also said her government will try to upgrade the trust-building process and reduce the deep-rooted suspicion between the two Koreas by building the practice of keeping promises that have been agreed upon. (Yonhap News)